I'm not sure what you mean about tags: I'm talking about simple javascript calls. You create the map, you create the marker, you create the infowindow all with references to those objects, and then you can arbitrarily link ANY user action to making the infowindow open on that marker by calling the appropriate methods. If you wanted to make a click event on some page element, ANY page element, trigger that behavior, then you'd attach a click event listener to that page element. Are you using a javascript library like jQuery? If so, it has a really simple way to do that:
<div id="pageelement">some text that when clicked on will fire the code to open the infowindow</div>
jQuery("#pageelement").click(function(){
execute some code (like the psuedocode I outlined above)